Technical Abstract:
A regional watershed scale project (Mississippi Delta Management Systems Evaluation Area) was established to assess effects of conservation land management practices on environmental quality. The focus was on three watersheds that drain into oxbow lakes (Thighman, Beasley, and Deep Hollow). Of the three watersheds, the greatest intensity of conservation practices was implemented at Deep Hollow (1996 to 2000), and the least at Thighman. Only edge-of-field practices (e.g., buffer strips, erosion control pipes) were used in Beasley watershed until 2000. All watersheds were primarily planted to cotton and soybean in 1996, but by 2002, land use patterns shifted substantially to include more corn, soybean, and in Beasley watershed, trees. Lake water was evaluated for herbicides (fluometuron, atrazine, cyanazine, and metolachlor), total solids, phytoplankton, and nutrients from 1996 to 2002. Water quality of the three watersheds was dynamic and was affected by land management practices and hydrology. Prior to initiation of improved practices, lake ecology was impaired in all lakes due to sedimentation. After management practices were implemented, primary productivity of lakes was restored. Overall, the highest sediment levels, algal and bacterial populations, enzyme activities and herbicide levels (atrazine and metolachlor for corn production) were observed in Thighman Lake. Implementation of reduced tillage and glyphosate resistant crops (cotton / soybeans) (after 2000) in Beasley watershed resulted in lower levels of suspended sediments and herbicide concentrations in lake water. Conversion of Deep Hollow watershed from conservation practices back to conventional tillage after 2000 increased levels of fluometuron in lake water with little effect on suspended sediment.